Elastomeric mountings have long been used for the primary suspension systems of railroad car trucks. Prior to the advent of these flexible mounting systems, wear surfaces were utilized as described in U.S. Pat. No. 4,785,740. The advantages of using elastomeric mountings over wear surfaces is described in U.S. Pat. Nos. 3,785,298, 4,483,253, 4,655,143, and 4,938,152 relating to self-steering railroad-car trucks. Following the invention of the basic self-steering truck, several developments led to improvements in the mountings themselves, as witnessed in several U.S. patents to be described later. These elastomeric mountings are positioned between the axle-box or axle-bearing adapter crown and side-frame-pedestal-jaw roof on a railroad-car truck. The elastomeric mountings provide controlled flexibility in all directions and have many advantages over the previously used metal to metal sliding surfaces or similar wear surfaces. These advantages include, reduced lateral and vertical shocks to the roller bearings, increased system damping, elimination of wear between the axle-box or axle-bearing adapter crown surface and the side-frame-pedestal-jaw roof, reduction in railroad-car wheel wear, reduced rail wear, improved life of truck components and bearings, and finally, elastomeric mounts provide for a squaring relationship between the railroad track and the railroad-car trucks.
Elastomeric mountings for railroad-car trucks can be made extremely stiff in compression for carrying large compressive loads resulting from railroad car and cargo weight, and yet remain flexible in shear for accommodating motions between the axle sets and the side-frames. The addition of controlled spring rates provides self-steering and controls vehicle dynamics. Patents have issued for many variations and improvements to these basic elastomeric mountings, and they generally fall into two categories. Patents which describe retrofittable mountings are described in U.S. Pat. Nos. 3,381,629; 3,638,582; 3,699,897; 4,363,278; and 4,674,412; and those which are generally directed toward highly sophisticated elastomeric mountings, where the elastomeric mounting and the railroad-car-pedestal jaw, axle-box or axle-bearing (hereinafter, the term axle-bearing will be used as the short hand for this alternative) adapter and attachment features evolved together are described in U.S. Pat. Nos. 4,416,203, 3,621,792, 4,026,217. The more difficult dilemma presents itself with the former group, where the elastomeric mounting must adapt to, improve, or retrofit the currently adequate three-piece, railroad-car truck. One embodiment of the present invention mounting has to be able to be used on new three-piece, railroad-car trucks, retrofit trucks which are currently in the field and have only wear surfaces, and replace the "prior art" limited service-life elastomeric mounting shown in FIG. 1.
The single-layer "prior art" elastomeric mounting shown therein is experiencing limited service-life due to elastomer degradation and disbonding at the free edge of the mounting. Although the "prior art" design lasts sufficiently long to offer an economic advantage for the railroads to use it, customers are demanding extended service life and have long sought such an advantage to further reduce operating costs.
Originally, the cause of the limited service life of the "prior art" configuration was not well understood. However, after much study and analysis by the inventor, the cause of the premature failures of the "prior art" mounting was determined. The previously unrecognized or misunderstood problem was a result of a low ratio of cocking stiffness to shear stiffness of the elastomeric mounting. The "prior art" mounting's cocking stiffness was so low as to allow the axle-bearing adapter crown to cock relative to the side-frame-pedestal-jaw roof during braking and railroad-car rocking. When applied braking forces tend to move the axles apart in the fore and aft direction, this deflection is taken up or accommodated in the "prior art" mounting. The rocking motion is due to hunting and other vehicle dynamics and causes lateral motions to be applied to the mounting. These lateral and fore and aft motions initially were thought to be accommodated by the "prior art" mounting as pure shear by those of skill in the art. However, because of the low cocking to shear stiffness ratio of the "prior art" design, the braking and rocking induces a combination of cocking and shear into the prior art mountings.
In fact, because of this low ratio, a high percentage of the motion is accommodated as cocking, when originally it was thought to be accommodated in shear. As a result of these high cocking motions, compression induced edge strains occur at the edges of the "prior art" mounting. These edge strains are directly responsible for the limited service-life of the "prior art" elastomeric mountings. Further, the described cocking motions tend to be much more detrimental to the service life of the mounting than pure shear motions would be. Therefore, it was determined that to increase the useful service-life, the cocking stiffness to shear stiffness ratio must be increased and the compression induced edge strains must be reduced by some means.